- [Bartosz Milewski's Blog](https://bartoszmilewski.com/)

- [_Categories For Programmers_](https://github.com/hmemcpy/milewski-ctfp-pdf/releases/download/v1.3.0/category-theory-for-programmers.pdf), which is selection of Bartosz's blog posts

- The [Comonad Reader Blog](http://comonad.com/reader/)

- [Philip Freeman's Blog](https://blog.functorial.com/)

- Papers

- [Wadler, _Theorems For Free!_ (1989)](https://ecee.colorado.edu/ecen5533/fall11/reading/free.pdf)
- [Meijer et al, _Functional Programming with Bananas, Lenses, Envelopes and Barbed Wire_ (1991)](https://maartenfokkinga.github.io/utwente/mmf91m.pdf)
- [Wadler, _Comprehending Monads_ (1990)](https://ncatlab.org/nlab/files/WadlerMonads.pdf)
- [Moggi, _Notions of Computation as Monads_ (1995)](https://core.ac.uk/download/pdf/21173011.pdf)
- [Rutten, _Automata and Coinduction (an exercise in coalgebra)_ (1998)](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.221.6957&rep=rep1&type=pdf)
- [McBridge et. al, _Applicative Programming With Effects_ (2008)](https://openaccess.city.ac.uk/id/eprint/13222/1/)
- [Hinze, _Reason Isomorphically!_, (2010)](http://www.cs.ox.ac.uk/people/daniel.james/iso/iso.pdf)
- [Pickering et. al, _Profunctor Optics_ (2012)](https://arxiv.org/ftp/arxiv/papers/1703/1703.10857.pdf)
- [Rivas et al., _Notions of Computation as Monoids_ (2014)](https://arxiv.org/pdf/1406.4823.pdf)
- [Jaskelioff, _A Representation Theorem For Second Order Functionals_ (2014)](https://arxiv.org/pdf/1402.1699.pdf)

- Haskell Libraries

- [`kan-extensions`](https://hackage.haskell.org/package/kan-extensions)
- [`fmlist`](https://hackage.haskell.org/package/fmlist)
- [`mmorph`](https://hackage.haskell.org/package/mmorph)
- [`free-categories`](http://hackage.haskell.org/package/free-categories-0.1.0.0)
- John Wiegley's [`coq-category`](https://github.com/jwiegley/category-theory), which isn't in Haskell but is a great formulation of category theory in a pure functional language